The present invention relates in general to structural supports for magnetic resonance imaging (MRI) apparatus and relates in particular to an open MRI apparatus having axially-spaced pairs of magnet coils supported by a pair of diametrically opposed supports.
An MRI magnet is characterized as open when there is an accessible, room temperature, physical gap provided between a pair of superconducting magnet coils. An open MRI magnet is desirable as it improves patient comfort and accessibility as compared to closed MRI magnets which many patients consider uncomfortable and which limit patient access.
In order to provide the desired openness and create an open gap around a patient imaging region, a pair of magnet coil assemblies can be separated into two axially-spaced half sections. The half sections of the magnet produce high attractive magnetic forces which must be reacted with a structural support system that separates and supports the half sections and prevents the magnet coils from collapsing upon one another.
Typical axial forces for a 1.0 T MRI magnet are in the range of about 160,000 lbs. (711 KN). Prior MRI support structures reacted these axial forces by an arrangement of axial posts which interconnected the two magnet half sections. The numerous posts limited the openness of the magnet.
An MRI support structure must not only axially separate and axially support the two magnet half sections during operation of the MRI apparatus, the support structure should also provide circumferential support to accommodate torsional or twisting forces which may be applied to the half sections during, for example, shipping, installation, mobile and normal operation. Moreover, it is desirable to provide such a support system which resists the transmission of floor-induced vibrations from the surrounding building structure to the MRI apparatus.
Accordingly, a need exists for a robust support structure for an open MRI apparatus which reacts high axial loads produced during operation of the apparatus, without adversely affecting the openness of the gap defined between two MRI magnet half sections.
A further need exists for such a structure which reacts tensile and compressive loads produced by a pair of MRI half sections as well as any torsional loads which may be applied to the half sections.
Another need exists for a support structure for an open MRI magnet assembly which resists the transmission of vibrations from the surrounding building floor.
The present invention has been developed to fulfill the needs noted above and therefore has as an object the provision of a support structure for axially separating and supporting a pair of superconducting magnet half sections without adversely affecting the openness of the patient gap defined between the two magnet half sections.
A further object of the invention is the provision of such a support structure which uses only two dramatically opposed supports for connecting together two MRI half sections to provide a high degree of openness with a minimum of patient obstruction.
Another object of the invention is to provide such a support structure which is compact in size.
Another object of the invention is the provision of a pair of axially-extending support assemblies having dissimilar or unequal constructions, dissimilar or unequal cross sections and which react loads differently.
Still another object of the invention is the provision of such a support structure which has very high bending, shear and torsional natural frequencies so as to make the MRI apparatus more tolerant to floor induced vibrations.
These and other objects are met by the present invention which is directed to a support structure for interconnecting and supporting a pair of half magnet sections of an MRI apparatus. The support structure includes two axially-extending supports or columns located diametrically opposite one another on the outer circumferential periphery of a pair of MRI magnet coil half sections. The opposed supports have unequal structural configurations and different cross sections and accommodate different types of loading.
The support with the larger cross section is advantageously constructed with a compressive load bearing member and one or more tension load bearing members. These compressive and tensile load bearing members react only a portion of the axial magnetic force produced between the two magnet half sections. The remainder of the load is reacted by a second, much smaller support member that reacts only compressive axial forces.
The larger support is radially offset to one side of the magnet assembly to enable the open magnet to maintain a high degree of openness and to improve patient comfort and accessibility. In order to provide for the flow of cryogenic fluid, such as liquid helium, between the two magnet half sections, at least the larger support includes a hollow fluid flow portion.
To further enhance the openness of the MRI system, the outer vacuum container can be formed with an inner and outer conical portion to further reduce encroachment of the structure into the region of the imaging gap.
Other objects, features and advantages of the present invention will be readily appreciated as the same becomes better understood after reading the subsequent description taken in conjunction with the accompanying drawings.